1. Field of the Invention
The present invention relates to a vibration preventing mechanism for a motor for rotating a turntable to which a disc is attached for reading information recorded on the disc and a disc apparatus using such a vibration preventing apparatus.
2. Description of the Related Art
A compact disc (having a diameter of 12 cm or 8 cm) which is reproduced by a laser pick-up is used as a recording medium for storing information such as database or software. In order to incorporate a disc apparatus using such a recording medium into a notebook-type personal computer having a reduced size, a built-in type CD-ROM drive unit which is incorporated into a housing of the notebook-type personal computer.
In a conventional apparatus, a tray on which a disc is placed is driven by a motor. That is, when the tray is moved outside a housing, a disc is placed on the turntable of the tray and, then, the tray is returned inside the housing by a drive force of the motor.
Reduction in size and thickness of a disc apparatus has been achieved by reducing not only the size of the tray and a driving mechanism for driving the tray but also the size of a pickup and the motor for rotating a turntable on which the disc is placed. Accordingly, a supporting structure for a rotational shaft of a motor for driving the turntable and the supporting structure for transmitting a torque to the rotational shaft receive an influence of the reduction in thickness.
In such a conventional disc apparatus, a rotational speed of the disc is increased up to twelve times or even sixteenth times faster than a standard speed so as to quickly read data (information) recorded on the disc. If the disc is rotated at such a high speed, a vibration is easily generated due to a center of gravity being slightly displaced from the center of rotation since a strength of supporting structures of the rotational shaft and a rotor in the motor for rotating the turn table is reduced.
For example, if the center of gravity of the disc is displaced from the center of rotation due to a displacement of a center hole or an uneven distribution of printing ink provided on a surface of the disc, a vibration is generated when the disc is rotated at a high speed. Such a vibration generated in the disc is transmitted to a pickup via the turntable and, thereby, the information recorded on the disc cannot be read by the pickup. In such a case, a control unit of the disc apparatus has to reduce the rotational speed of the motor for driving the turntable which results in a reduction in the reading speed.
Accordingly, there is a problem in that the reading speed cannot be increased even when the rotational speed of the disc can be increased twelve times or sixteen times faster than the standard speed since the rotational speed of the disc is decreased to a speed at which a vibration is not generated.
Additionally, if the vibration of the disc is transmitted to a base which supports the motor via the turntable and the motor, the vibration may be transmitted also to a housing of the notebook-type personal computer. Thus, there is a problem in that such a vibration provides an unpleasant feel to an operator or a movable part such as a tray vibrates, which results in generation of a rattling noise.